1. Field of the Invention
This invention relates to a magnetic disk cartridge in which a disk-shaped thin magnetic recording medium, namely, a magnetic disk sheet, is rotatably supported. The invention relates more particularly to a magnetic disk cartridge having an improved cleaning liner which is brought into contact with the surface of the sheet to clean and protect the surface of the sheet.
2. Background Art
In general, writing data on the magnetic disk sheet or reading data out of the disk sheet is carried out by slidably moving the writing head or reading head radially of the sheet which is being rotated. Therefore, if, in writing data into the magnetic disk sheet or reading data out of the magnetic disk sheet, dust, foreign matter or other particles are on the surface of the magnetic disk sheet, then the data are erroneously written on the magnetic sheet or read out of the disk sheet. That is, so-called "dropout" occurs. This difficulty is very serious because the magnetic disk cartridge is employed mainly as the digital data memory of a computer or the like.
Accordingly, the enclosing case of a conventional magnetic disk cartridge is made of relatively flexible pressed paper or synthetic resin or hardened synthetic resin, and an opening is provided into the case having a dust-proof shutter. Furthermore, a cleaning liner is provided on the inner wall of the case in such a manner that the liner is in light contact with the recording surface of the magnetic disk sheet. The liner acts to wipe the dust off the surface of the magnetic disk sheet which is being rotated. That is, the liner is used to clean the surface of the magnetic disk sheet.
The liner is made of unwoven cloth of rayon fibers and polypropylene or polyester compound fibers. However, the unwoven cloth suffers from the following difficulties.
When the unwoven cloth is manufactured, fiber pellets are formed by thermal fusion. When the unwoven cloth is torn or trapped, fine particles, such as fibers, are scattered from the unwoven cloth. Furthermore, when the liner is set between the upper half and the lower half in order to weld the upper and lower halves together by ultrasonic welding to form a magnetic disk cartridge, or when vibration or impact is applied to a magnetic disk cartridge in various manners, pellets of polypropylene or the like fall on the surface of the magnetic disk sheet and enter the head gap or rub the surface of the magnetic disk sheet. As a result, the pellets or the like cause temporary or permanent dropout.
In order to eliminate this difficulty, a method has been employed in which binder is applied to the liner to increase the strength of the surfaces of the liner. The method suffers from the difficulties that, as the binder is uniformly applied to the entire liner, the cushioning characteristic of the liner is worsened, and accordingly so is the cleaning characteristic.